1. Field of the Invention
The present invention relates to the detection of faults within a fiber optic network and the determination of the location of the detected fault and more specifically to the method and apparatus to determine the presence of, and location of, a fiber network fault, within a single optical fiber strand, utilizing, in particular, a transceiver that operates as both a digital bi-directional data transport on the same fiber, and a micro optical time-domain reflectometer (μOTDR).
2. Description of the Prior Art
In general terms, the detection of communication line faults has been a concern in the art for a long time. The advent of the communication age was accompanied by the proliferation of the necessary wires and cables to support that communication. As the communication networks grew larger, so too did the lengths of wires, cables, and now fiber optic lines, which now comprise networks thousands of kilometers in length. These wires, cables and optical fibers may be damaged for a number of reasons and need repair. Pinpointing the location of a fault is valuable information, regardless of whether the network is just a few meters or a few thousand meters in length.
The following are some examples of prior art fault detection devices:
U.S. Pat. No. 4,449,247 issued to Waschka (hereafter the “Waschka Patent”) depicts a system that transports additional data regarding the local status of each terminal, between the different terminals of a communication system. Unlike the present invention, the Waschka Patent does not check the status of the optical fiber or the location of a fault in the fiber, but merely has each station send out its own status to its neighboring terminal, receive status from a neighboring terminal and create separate alarms based on the various status notices. Additionally, the Waschka Patent recognizes only that it lost data and cannot determine if there is an electronic failure, a fiber failure, or a failure with the detector. Further, the Waschka Patent does not measure the distance to any fiber that is broken or determine if a fault is a fiber failure or an electronic failure. The Waschka Patent is merely a generic structure that sends and reads status reports to and from the various terminals without doing any type of analysis.
U.S. Pat. No. 5,586,251 issued to James A. Coleman et al. and assigned to the United States of America as represented by the Secretary of the Army on Dec. 17, 1996 for “Continuous On-Local Area Network Monitor” (hereafter the “Coleman Patent”), discloses a high level monitoring system of interconnected instruments having a plurality of connections to transmit and receive data regarding the status of the various segments of the system, including a preamble to notify the system that the following is not data. The Coleman Patent transmits information, doesn't look at the reflection of light and requires a plurality of transceivers and is incapable of detection by the transmission and receiving of light and using same to determine the location of a fault within the optic fiber itself.
U.S. Pat. No. 6,385,561 issued to John James Soraghan (hereafter the Soraghan Patent”) discloses detecting faults in electrical cables by coupling signals and comparing them and having separate input and output leads. The Soraghan Patent applies this same detection technique of coupling and comparing signals to fiber optic cables and storing sample signals. Soraghan is incapable of detecting a fault utilizing only one fiber and without any sampling, storage or comparisons.
U.S. Pat. No. 6,714,021 issued to Emrys J. Williams (hereafter the “Williams Patent”) discloses detecting faults within an electrical system by using electrical impedance and further requires a center plane, a back plane and a second back plane. The Williams Patent cannot be used for an optical circuit.
U.S. Pat. No. 7,139,668 issued to Eric Robert Bechhoefer (hereafter the “Bechhoefer Patent”) discloses the utilization of storing digitized electrical reflections and scoring them to determine the presence of an event. The Bechhoefer Patent is designed for a cable system, not a fiber optic system, and utilizes different components to transmit and receive than it does to determine an event in the system.
U.S. Pat. No. 7,218,388 issued to Gordon A. Keeler et al. and assigned to Sandia Corporation on May 15, 2007 for “VSCEL Fault Location Apparatus And Method” (hereafter the “Keeler Patent”) discloses the use of the same light source that transmits the light to also detect a reflection. Additionally, the Keeler Patent discloses the addition of an electronic circuit that changes the bias, and hence performance and characteristics, of the device, in order to perform a fault detection. Additionally, the transmitter in the Keeler Patent cannot, in normal operation, transmit and receive data, it can only transmit. The Keeler transmitter can receive data after a first and a second bias has been applied, after which it cannot transmit until the biases have been removed. The Keeler Patent does not have a data receiver in its system.
U.S. Pat. No. 7,239,680 issued to Sang T. Bui (hereafter the “Bui Patent”) discloses a method to diagnose an electrical system utilizing adaptive coefficients as filters which is used to determine the status of the cables as either open or short. An optic fiber doesn't have shorts, thus the Bui Patent cannot be used for fiber optic systems.
U.S. Pat. No. 7,558,212 issued to Jerome Edwin Olinski (hereafter the “Olinski Patent”), discloses a method for performing diagnostics by comparing the signal to stored data. Additionally, the Olinski Patent has mapped out and stored the physical locations of points along its pathway and it is to one of these points that the Olinski Patent directs a user as the location of the fault. In other words, the Olinski Patent requires prior knowledge of everything on its line, to which it then matches the response signal with the cable information and thus gives, as the location of the fault, the location of the nearest physical object on its line.
An Article dated February 1995 from the Hewlett-Packard Journal by Frank A. Maier and Harald Seeger entitled “Automation of Optical Time-Domain Reflectometry Measurements” (hereafter the “Hewlett Packard Article”) discloses the use of an OTDR which must be physically attached to each cable one at a time for testing for faults, whether by switching the lines internally or physically reconnecting the OTDR to the fiber. The Hewlett Packard Article does not teach that the same unit that is used to detect the fault is also used to transmit data.